As is known in the art, carbon black is a very useful commodity and is obtained from many resources. Among the valuable uses of carbon black is in the production of rubber tires. As a matter of fact, outside of rubber, the major portion of rubber tires is carbon black, and it would be very desirable if such carbon black contained in rubber tires could be reused again. The recycling of carbon black and obtaining useful products from rubber contained in tires serves a two-fold purpose: first, it would conserve our valuable resources and, second, it would ease the problem of what to do with discarded rubber tires. For example, at least two hundred million rubber tires are discarded in the United States every year. And, although such tires make up a relatively small fraction of the solid waste, tires are very difficult to dispose of.
When rubber tires are burned, they give off large quantities of unburned hydrocarbons which are highly visible and noxious. Moreover, the problem of disposing of scrap rubber tires is not solved by using the tires as land fill because tires are resistant to natural decomposition and eventually emerge at the surface of the land fill where their appearance is objectionable.
Another approach to the problem of what to do with discarded rubber containing carbon black, for example, rubber tires, is to pyrolyze the rubber tires to obtain valuable hydrocarbons therefrom. However, after the hydrocarbons are removed, a great deal of solid material remains, said solid material (usually called char) being composed primarily of carbon black and inorganic material primarily composed of zinc and sulfur. Carbon black cannot be successfully reused to make, for example, rubber tires, unless such inorganic material is removed from the carbon black. Moreover, since the primary metal included within the inorganic material is zinc, normally as zinc oxide, it is desirable to remove the zinc in order to render the solid char reusable in producing rubber tires, and, at the same time, recovering the zinc in order to be able to reuse this valuable metal.